1. Field of the Invention
The present invention relates to a multi-beam interferometer displacement measuring system, and more particularly to a multi-beam interferometer displacement measuring system utilized in a large measuring range. The multi-beam interferometer displacement measuring system is insensitive to the tilt angle and the environmental disturbances and can realize the high precision displacement in a large measuring range under an uncomplicated measuring condition.
2. Description of Related Art
To develop high resolution of the conventional measuring system or apparatus is the focal point of research in the precision industries and the photoelectric enterprises. A conventional photoelectric measuring apparatus can be classified into two kinds based on the measuring method: one is a laser interferometer and the other is an interferometric range finder. The conventional interferometric range finder further has a homodyne multi-beam interferometer and a heterodyne multi-beam interferometer. The conventional homodyne multi-beam interferometer may be a Michelson interferometer (with a resolution of 1.24 nanometers), has an uncommon optical path structure and will be sensitive to the environmental disturbances and the thermal current effect of temperature and this will affect the visibility of the interferential stripes.
The conventional heterodyne multi-beam interferometer has a common optical path structure and is resistive to the environmental disturbances and vibrations. With reference to FIG. 6, a Fabry-Perot interferometer 60 is one kind of the conventional multi-beam interferometers and is used to measure displacement by two approximately parallel planar mirrors 61, 62. Multiple interferential stripes will be distinctly formed between the planar mirrors 61, 62 of the conventional Fabry-Perot interferometer 60 and this can enable the positions of the interferential stripes to measure displacement precisely. Consequently, the resolution and the measuring precision of the conventional Fabry-Perot interferometer 60 will be better than that of the conventional homodyne multi-beam interferometer.
When the measuring distance between the planar mirrors 61, 62 of the conventional Fabry-Perot interferometer 60 is too long (if the measuring distance between the planar mirrors 61, 62 is at the scale of micrometer), the planar mirrors 61, 62 will not be parallel with each other and will form a tilt angle between the planar mirrors 61, 62. However, the tilt angle will alter the intervals and the contrast of the interferential stripes formed between the planar mirrors 61, 62 of the conventional Fabry-Perot interferometer 60 and this will affect the accuracy of the measuring result. Thus, the measuring range of the conventional Fabry-Perot interferometer 60 is constrained in micrometers and is hard to perform displacement measurement in the large range.
A multi-beam interferometer displacement measuring system utilized in a large measuring range in accordance with the present invention mitigates or obviates the aforementioned problems.